Setting-up DHCP on Cisco Routers

The Dynamic Host Configuration Protocol (DHCP) provides the capability to automatically allocate reusable network addresses and configuration options to hosts.

DHCP messages are based on the format of BOOTP messages and as so the two are interoperable, however, DHCP does not require the DHCP server to be configured with the MAC addresses of all clients. DHCP automatically assigns an IP address from a pool of valid IP addresses in the respective subnet.

Also, since the DHCP server can maintain configurations for several subnets, you only need to update the respective server when you need to change configuration parameters.

For this lab, I create a very simple setup with a router connected to a layer 2 switch that has four hosts connected to it. I use a Cisco 2126XM router [IOS Version 12.2(28)] as the layer 3 device and a Cisco WS-C2960-24TT switch [IOS Version 12.2(25)FX] as the layer 2 device. The four hosts that connect to the switch have not been configured with any IP addresses. The network diagram is shown below.

Network diagram for Cisco DHCP lab topology

All I need to do for this setup is configure DHCP on the Cisco 2126XM router as shown below. I also make sure to exclude the DHCP server’s IP address from the address pool and further exclude four more IP addresses just for demonstration purposes.

Configuring DHCP on a Cisco Router